Synthesis and biological evaluation of heterocyclic structures targeting underexplored targets

Tremendous improvements in the field of genomics and molecular biology have accelerated the identification of various targets that can be used in drug discovery programs. Over 22000 genes were identified after sequencing of the human genome from which an estimated 5000 have a disease modulating effect. This paved the way for the design and synthesis of drugs against a selected target, instead of relying on the desired effect as in a phenotypic screening. However, only a fraction of the estimated available targets has been explored and is currently pursued as drug target. In this PhD thesis, the synthesis and biological evaluation of small molecule ligands for three underexplored targets is described. In Chapter 2, adaptor protein 2 associated kinase 1 (AAK1) was chosen as a target for the development of antiviral agents. AAK1 plays a crucial role in the regulation of the clathrin mediated endocytosis, which is an integral part of the viral lifecycle of several unrelated viruses like dengue virus and Ebola virus. Since AAK1 is a host protein, AAK1 inhibitors offer the possibility of developing broad spectrum antivirals, and, in addition, the emergence of resistance is less of an issue. A known pyrrolo [2,3-b]pyridine analogue was selected as starting point for an optimization campaign for increasing its potency in both the binding and in vitro antiviral assay against the dengue and ebola virus. Furthermore, it was demonstrated that AAK1 inhibition was an important mechanism in the antiviral activity of these compounds. These findings establish the potential of AAK1 inhibitors as treatment of currently untreatable viral threats. Chapter 3 relied on Mas-related gene receptor X2 (MRGPRX2) as the target of choice. This G-protein coupled receptor (GPCR) is primarily expressed in the dorsal root ganglia and on mast cells. Stimulation of MRGPRX2 leads to an IgE-independent degranulation of mast cells. Therefore, MRGPRX2 antagonists hold promise for the treatment of various allergic diseases like asthma and chronic urticaria. A compound library of over 1600 heterocycles was screened for MRGPRX2 antagonistic activity yielding four hits based on a benzo[4,5]imidazo[1,2-a]pyrimidin-4(10H)-one scaffold. These hits were systematically optimized to increase their potency as MRGPRX2 antagonists, affording three new analogues with activity in the low nanomolar range. Finally, Chapter 4 introduced the cluster chemokine receptor 8 (CCR8) as drug target. This GPCR is involved in the migration of immune cells (especially regulatory T-cells) to infection hearths. CCR8 is unique amongst its peers that it is the sole receptor for CCL1. Furthermore, it has been established that CCR8 inhibition in the tumor microenvironment correlates with an increased survival of cancer patients. In contrast, in the mouse encephalitis model, a generally accepted in vivo model for multiple sclerosis, administration of CCL1 and subsequent activation of CCR8 suppresses this autoimmune disease, underpinning the role of CCR8 in autoimmune modulation. Therefore, a known CCR8 agonist with moderate CCR8 affinity was subjected to a systematic optimization in order to increase its potency in the CCR8 binding and calcium mobilization assay.status: publishe